1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used as a transmission for a car or as a transmission for various kinds of industrial machines.
2. Description of the Related Art
Conventionally, it has been studied that such a toroidal-type continuously variable transmission as shown schematically in FIGS. 7 and 8 is used as a transmission for a car. In this toroidal-type continuously variable transmission, for example, as disclosed in JP-A-62-71465U, an input side disk 2 is supported concentrically with an input shaft 1, while an output side disk 4 is fixed to the end portion of an output shaft 3 which is disposed concentrically with the input shaft 1. In the interior portion of a casing in which the toroidal-type continuously variable transmission is stored, there are disposed trunnions 6, 6 which are capable of swinging about their associated paired pivot shafts 5, 5 disposed at a torsional position with respect to the input and output shafts 1 and 3: specifically, the torsional position is a position which does not intersect the center axes of the input side and output side disks 2, 4 and are perpendicular to the directions of the center axes of the input side and output side disks 2, 4.
That is, in each of the trunnions 6, 6 which is disposed in the portion that is shifted from the center axes of the two disks 2, 4, on the outer surfaces of their respective two end portions, there are disposed the paired pivot shafts 5, 5 in such a manner that they extend at right angles to the directions of the center axes of the two disks 2, 4 and are concentric with each other. Also, on the middle portions of the trunnions 6, 6, there are supported the base end portions of displacement shafts 7, 7; and, the inclination angles of the displacement shafts 7, 7 can be adjusted by swinging the trunnions 6, 6 about their respective paired pivot shafts 5, 5. On the peripheries of the displacement shafts 7, 7 thus supported on the trunnions 6, 6, there are rotatably supported power rollers 8, 8. And, the power rollers 8, 8 are held by and between the mutually opposing inner surfaces 2a, 4a of the input side and output side disks 2, 4. Each of the inner surface 2a, 4a has a cross section formed as a concave surface which can be obtained when an arc having the pivot shaft 5 as the center thereof is rotated. And, the peripheral surfaces 8a, 8a of the power rollers 8, 8, which are respectively formed as spherically convex surfaces, are contacted with the inner surfaces 2a, 4a.
Between the input shaft 1 and input side disk 2, there is disposed a loading cam device 9; that is, the loading cam device 9 is capable of driving the input side disk 2 rotationally while pressing the input side disk 2 elastically toward the output side disk 4. The loading cam device 9 is composed of a loading cam 10 rotatable together with the input shaft 1, and a plurality of (for example, four) rollers 12, 12 which are rollably held by a retainer 11. On one side surface (in FIGS. 7 and 8, the right surface) of the loading cam 10, there is formed a cam surface 13 which is a curved surface extending in the circumferential direction of the loading cam 10; and, on the outer surface (in FIGS. 7 and 8, the left surface) of the input side disk 2 as well, there is formed a cam surface 14 having a similar shape to the cam surface 13. And, the plurality of rollers 12, 12 are supported in such a manner that they can be rotated about their respective axes extending in the radial direction with respect to the center of the input shaft 1.
When the above-structured toroidal-type continuously variable transmission is in use, in case where the loading cam 10 is rotated as the input shaft 1 is rotated, the cam surface 13 presses the plurality of rollers 12, 12 against the cam surface 14 formed on the outer surface of the input side disk 2. As a result of this, the input side disk 2 is pressed against the plurality of power rollers 8, 8 and, at the same time, due to the mutual pressing actions between the two cam surfaces 13, 14 and the plurality of rollers 12, 12, the input side disk 2 is rotated. And, the rotation of the input side disk 2 is transmitted through the plurality of power rollers 8, 8 to the output side disk 4, so that the output shaft 3 fixed to the output side disk 4 can be rotated.
Now, description will be given below of a case where a rotation speed ratio (transmission ratio) between the input shaft 1 and output shaft 3 is changed. At first, when reducing the rotation speed ratio between the input shaft 1 and output shaft 3, the trunnions 6, 6 may be respectively swung in a given direction about their respective paired pivot shafts 5, 5. And, the displacement shafts 7, 7 maybe inclined respectively in such a manner that the peripheral surfaces 8a, 8a of the power rollers 8, 8, as shown in FIG. 7, can be respectively contacted with the near-center portion of the inner surface 2a of the input side disk 2 and the near-outer-periphery portion of the inner surface 4a of the output side disk 4. On the other hand, when increasing the rotation speed ratio between the input shaft 1 and output shaft 3, the trunnions 6, 6 may be respectively swung in the opposite direction to the given direction about their respective paired pivot shafts 5, 5. And, the displacement shafts 7, 7 may be inclined respectively in such a manner that the peripheral surfaces 8a, 8a of the power rollers 8, 8, as shown in FIG. 8, can be respectively contacted with the near-outer-periphery portion of the inner surface 2a of the input side disk 2 and the near-center portion of the inner surface 4a of the output side disk 4. Also, in case where the inclination angles of the displacement shafts 7, 7 are set in the intermediate angles between the angles shown in FIGS. 7 and 8, there can be obtained an intermediate transmission ratio between the input and output shafts 1, 3.
Also, FIGS. 9 and 10 show an example of a more specifically structured toroidal-type continuously variable transmission which is disclosed in JP-A-1-173552U. An input side disk 2 serving as a first disk and an output side disk 4 serving as a second disk are respectively supported on the periphery of a cylinder-like input shaft 15 serving as a rotary shaft in such a manner that they can be rotated through needle roller bearings 16, 16. That is, in the respective central portions of the input side and output side disks 2, 4, there are formed through holes 17, 17 each having a circular cross section in such a manner that they respectively extend through the inside and outside surfaces of the input side and output side disks 2, 4 in the axial direction (in FIG. 9, in the right and left direction) of the disks 2, 4. The needle roller bearings 16, 16 are respectively interposed between the inner peripheral surfaces of the through holes 17, 17 and the outer peripheral surface of the middle portion of the input shaft 15. In the inner peripheral surfaces of the near-inside-surface end portions of the through holes 17, 17, there are formed securing grooves 18, 18; and, retaining rings 19, 19 are secured to the securing grooves 18, 18 respectively to thereby prevent the needle roller bearings 16, 16 from slipping out from their respective through holes 17, 17 toward the inside surfaces 2a, 4a of the input side and output side disks 2, 4. Also, the loading cam 10 is spline engaged with the outer peripheral surface of the end portion (in FIG. 9, the left end portion) of the input shaft 15; and, a flange portion 20 of the loading cam 10 prevents the thus engaged loading cam 10 from moving in a direction where it parts away from the input side disk 2. And, the loading cam 10 and rollers 12, 12 cooperate together in forming a loading cam device 9 which, based on the rotation of the input shaft 15, can rotate the input side disk 2 while pressing the input side disk 2 toward the output side disk 4. An output gear 21 is engaged with the output side disk 4 through keys 22, 22, so that the output side disk 4 and output gear 21 are allowed to rotate in synchronism with each other.
The respective two end portions of the pair of trunnions 6, 6 are supported on a pair of support plates 23, 23 in such a manner that they can be swung and also can be shifted in the axial direction (in FIG. 9, in the front and back direction; in FIG. 10, in the right and left direction). And, the displacement shafts 7, 7 are supported in circular holes 24, 24 respectively formed in the middle portions of the trunnions 6, 6. The displacement shafts 7, 7 respectively include support shaft portions 25, 25 and pivot shaft portions 26, 26 which are arranged in parallel to and eccentrically to each other. Of these shaft portions, the support shaft portions 25, 25 are rotatably supported on the interior portions of the circular holes 24, 24 through radial needle roller bearings 27, 27. Also, the power rollers 8, 8 are rotatably supported on the peripheries of the pivot shaft portions 26, 26 through another radial needle roller bearings 28, 28.
By the way, the pair of displacement shafts 7, 7 are disposed at 180.degree. opposite positions to the input shaft 15. Also, the directions, in which the pivot shaft portions 26, 26 of the displacement shafts 7, 7 are eccentric to the support shaft portions 25, 25, are the same directions as the rotation directions (in FIG. 10, left and right opposite directions) of the input side and output side disks 2, 4. Also, the eccentric direction is set as a direction which is almost perpendicular to the mounting direction of the input shaft 15. Therefore, the power rollers 8, 8 are supported in such a manner that they can be shifted slightly along the mounting direction of the input shaft 15. As a result of this, even when, due to the elastic deformation of the component members caused by large loads applied to the component members during the transmission of the rotational force, the power rollers 8, 8 tend to shift in the axial direction of the input shaft 15 (in FIG. 9, in the left and right direction; in FIG. 10, in the front and back direction), such shift can be absorbed without applying unreasonable forces to the respective component members.
Also, the end portion of the input shaft 15 is supported on the fixed portion of the interior of the casing by a pair of ball bearings 44, 44 respectively of an angular type in such a manner that it can be rotated as well as can be shifted in the axial direction of the input shaft 15. And, a loading nut 38 is fixed to the portion of the end portion of the input shaft 15 that projects from the two ball bearings 44, 44. Between the loading nut 38 and the ball bearing 44 to which the loading nut 38 is opposed, there is interposed a belleville spring 39 which is an elastic member. The belleville spring 39 pulls the input side disk 2 elastically to the right in FIG. 9 through the input shaft 15 and loading cam device 9; and, also when the loading cam device 9 is not in operation, the belleville spring 39 has a function to secure the contact pressure between the inner surfaces 2a, 4a of the two disks 2, 4 and the peripheral surfaces 8a, 8a of the power rollers 8, 8.
Also, between the outside surfaces of the power rollers 8, 8 and the inside surfaces of the middle portions of the trunnions 6, 6, there are interposed thrust ball bearings 29, 29 and thrust needle roller bearings 30, 30 in this order starting from the outside surfaces of the power rollers 8, 8. Of these bearings, the thrust ball bearings 29, 29 are structured such that, while receiving thrust-direction loads applied to the power rollers 8, 8, they allow the rotation of the power rollers 8, 8. Also, the thrust needle roller bearings 30, 30 are structured such that, while receiving thrust loads applied to outer races 31, 31 forming the thrust ball bearings 29, 29 from the power rollers 8, 8, they allow the pivot shaft portions 26, 26 and outer races 31, 31 to oscillate about the support shaft portions 25, 25.
Further, drive rods 32, 32 are respectively connected to the respective one end portions (in FIG. 10, the left end portions) of the trunnions 6, 6, while drive pistons 33, 33 are respectively fixed to the outer peripheral surfaces of the middle portions of these drive rods 32, 32. And, the drive pistons 33, 33 are respectively fitted into drive cylinders 34, 34 in an oil-tight manner.
In the above-structured toroidal-type continuously variable transmission, the rotation of the input shaft 15 is transmitted through the loading cam device 9 to the input side disk 2. And, the rotation of the input side disk 2 is transmitted through a pair of power rollers 8, 8 to the output side disk 4 and, further, the rotation of the output side disk 4 is taken out from the output gear 21. To change a rotation speed ratio between the input shaft 15 and output gear 21, the pair of drive pistons 33, 33 may be shifted in the mutually opposite directions. With the shifting movements of the pistons 33, 33, the pair of trunnions 6, 6 are shifted in the mutually opposite directions; for example, the power roller 8 situated on the lower side in FIG. 10 is shifted to the right in FIG. 10, while the power roller 8 on the upper side in FIG. 10 is shifted to the left in FIG. 10. This changes the direction of tangential-direction forces acting on the contact portions between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4. With the change in the tangential-direction force direction, the trunnions 6, 6 are caused to swing in the mutually opposite directions about the pivot shafts 5, 5 pivotally supported on the support plates 23, 23. As a result of this, as shown in FIGS. 7 and 8 which have been discussed before, the contact positions between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4 are caused to change, thereby changing the rotation speed ratio between the input shaft 15 and output gear 21.
By the way, when carrying out the transmission of the rotation force between the input shaft 15 and output gear 21 in this manner, due to the elastic deformation of the component members, the power rollers 8, 8a reshifted in the axial direction of the input shaft 15, so that the displacement shafts 7, 7 pivotally supporting the power rollers 8, 8 are slightly rotated about their respective support shaft portions 25, 25. As a result of this slight rotation, the outside surfaces of the outer races 31, 31 of the thrust ball bearings 29, 29 and the inside surfaces of the trunnions 6, 6 are shifted with respect to each other. Because the thrust needle roller bearings 30, 30 are interposed between these outside surfaces and inside surfaces, such relative shifting motion can be achieved with a small force. Therefore, the inclination angles of the displacement shafts 7, 7 can be changed in the above-mentioned manner with a small force.
Further, conventionally, as disclosed in JP-A-1-234646, JP-A-7-158711, JP-A-8-21503, and JP-A-8-35549, there is also known a so called double cavity type structure in which, in order to increase the torque that can be transmitted, as shown in FIGS. 11 and 12, on the periphery of an input shaft 15a, there are disposed two input side disks 2A, 2B and two output side disks 4, 4, while these two input side disks 2A, 2B and two output side disks 4, 4 are arranged in parallel to each other with respect to the power transmission direction. In the structure shown in FIGS. 11 and 12, on the periphery of the middle portion of the input shaft 15a, there is supported an output gear 21a in such a manner that it can be rotated with respect to the input shaft 15a, while the two output side disks 4, 4 are respectively spline engaged with the two end portions of a cylindrical-shaped sleeve 35 disposed on the central portion of the output gear 21a. And, between the inner peripheral surfaces of through holes 17, 17 formed in the two output side disks 4, 4 and the outer peripheral surface of the input shaft 15a, there are interposed needle roller bearings 16, 16, whereby the two output side disks 4, 4 are respectively supported on the periphery of the input shaft 15a in such a manner that they can be rotated with respect to the input shaft 15a as well as can be shifted in the axial direction of the input shaft 15a. Also, the two input side disks 2A, 2B are respectively supported on the two end portions of the input shaft 15a in such a manner that they can be rotated together with the input shaft 15a. The input shaft 15a can be driven, that is, rotated by a drive shaft 36 through a loading cam device 9. By the way, between the outer peripheral surface of the leading end portion (in FIGS. 11 and 12, the right end portion) of the drive shaft 36 and the inner peripheral surface of the base end portion (in FIGS. 11 and 12, the left end portion) of the input shaft 15a, there is interposed a radial bearing 37 such as a sliding bearing or a needle roller bearing. Therefore, the drive shaft 36 and input shaft 15a are combined together in such a manner that they can be slightly shifted in the rotation direction thereof while they are still left arranged concentric with each other.
However, one input side disk 2A (in FIGS. 11 and 12, the input side disk that is situated on the right side) is disposed such that its back surface (in FIGS. 11 and 12, its right side surface) is butted against a loading nut 38a through a belleville spring 39a having large elasticity, thereby substantially preventing the one input side disk 2A from shifting in its axial direction (in FIGS. 11 and 12, in the right and left direction) with respect to the input shaft 15a. On the other hand, the other input side disk 2B, which is disposed opposed to a loading cam 10, is supported on the input shaft 15a by a ball spline 40 in such a manner that it can be shifted in the axial direction thereof. And, between the outside surface (in FIGS. 11 and 12, the left side surface) of the input side disk 2B and a securing stepped portion 41 formed on the outer periphery of the middle portion of the input shaft 15a, there is interposed a belleville spring 42 which serves as a pre-load spring. The belleville spring 42 has elasticity smaller than that of the belleville spring 39 and applied pre-loads to the contact portions between the inner surfaces 2a, 4a of the disks 2A, 2B and the peripheral surfaces 8a, 8a of the power rollers 8, 8. That is, when the loading cam device 9 does not generate thrust or when it generates only small thrust, the belleville spring 42 secures the contact pressures of the contact portions to thereby allow the toroidal-type continuously variable transmission to transmit small torque as well.
Also, the output gear 21a is rotatably supported on a partition wall 43 formed in the interior portion of a housing in such a manner that it is prevented from shifting in the axial direction thereof by a pair of ball bearings 44a, 44a each of an angular type. By the way, in the toroidal-type continuously variable transmission of a double cavity type shown in FIGS. 11 and 12, as described above, one or both of the input side disks 2A, 2B disposed opposed to the loading cam 10 are supported on the input shaft 15a by the ball splines 40, 40 in such a manner that they can be shifted in the axial direction thereof. The reason for this is to allow the two disks 2A, 2B to shift in the axial direction thereof with respect to the input shaft 15a due to the elastic deformation of the component members caused by the operation of the loading cam device 9 while rotating the two disks 2A, 2B in synchronism with each other. Also, the reason why the back surface of one input side disk 2A is butted against the loading nut 38a through the belleville spring 39 having large elasticity is to absorb a thrust-direction shock load applied to one input side disk 2A when the torque transmitted through the toroidal-type continuously variable transmission increases suddenly.
When the above-mentioned toroidal-type continuously variable transmission of a double cavity type is in operation, the rotation of the drive shaft 36 is transmitted through the loading cam device 9 to the other input side disk 2B (in FIGS. 11 and 12, situated in the left side) and, further, the rotation of the input side disk 2B is transmitted through the input shaft 15a to one input side disk 2A, so that the two input side disks 2A, 2B can be rotated in synchronism with each other. And, the rotational movements of the two input side disks 2A, 2B are respectively transmitted to the pair of output disks 4, 4 through a plurality of power rollers 8, 8 for each disk (in the illustrated structure, two power rollers for each disk, that is, four power rollers in total) . As a result of this, the sleeve 35, whose two end portions are spline engaged with the two output side disks 4, 4, is rotated to thereby rotate the output gear 21a fixed to the outer peripheral surface of the middle portion of the sleeve 35. As described above, in the toroidal-type continuously variable transmission of a double cavity type, since the transmission of the rotation from the drive shaft 36 to the output gear 21a is carried out through two systems arranged parallel to each other, large torque transmission is possible. Also, by changing the inclination angles of the power rollers 8, 8 held by and between the disks 2A, 2B and 4, 4 in synchronism with each other, a transmission ratio between the two input side disks 2A, 2B and the two output side disks 4, 4 can be changed.
In the conventional toroidal-type continuously variable transmission which is structured and operates in the above-mentioned manner, sufficient consideration is not always given to the durability of the loading nut 38 or 38a which is to be threadedly engaged with and fixed to the input shaft 15 or 15a serving as a rotary shaft. That is, of the conventional structures, in the structure shown in FIG. 9, the belleville spring 39, which is disposed adjacent to the loading nut 38, is elastically deformed according to the operating state of the loading cam device 9 (according to the intensity of a thrust load generated), with the result that part of the belleville spring 39 and the axial-direction one surface (in FIG. 9, the left side surface) of the loading nut 38 are caused to rub against each other. Also, in the structure shown in FIGS. 11 and 12 as well, although not so much as in the structure shown in FIG. 9, the belleville spring 39a is elastically deformed according to the operating state of the loading cam device 9, with the result that part of the belleville spring 39a and the axial-direction one surface (in FIGS. 11 and 12, the left side surface) of the loading nut 38a rub together.
In order to prevent the loading nut 38 or 38a from being worn heavily in spite of the fact that it rubs against the belleville spring 39 or 39a, it is necessary to enhance (harden) the hardness of the loading nut 38 or 38a. On the other hand, in order to prevent the loading nut 38 or 38a threadedly engaged with the input shaft 15 or 15a from shifting from its given position, it is necessary that, after the loading nut 38 or 38a is threadedly engaged with the given portion of the input shaft 15 or 15a, apart of the loading nut 38 or 38a is fastened inwardly in the diameter direction thereof to thereby prevent the loosening of the loading nut 38 or 38a. To fasten part of the loading nut 38 or 38a inwardly in the diameter direction thereof, it is necessary that the hardness of the load nut 38 or 38a is lowered (softened) to thereby prevent occurrence of damage such as a crack in the loading nut 38 or 38a which could be otherwise caused by the fastening operation.
However, in the conventional toroidal-type continuously variable transmission, due consideration is not given to fulfillment of such two contrary requirements, that is, wear prevention and damage prevention in the fastening operation.